'96 C280 Engine Issues (idle,throttle,acceleration). Help!!
 

I own a '96 C280 with 120k miles and have recently been having a problem with the engine. Intermittently, the engine:

1) revs the RPM's while at a complete stop; or
2) cuts out during acceleration or at speed.

I've been searching the forum posts for the last several weeks and the general diagnosis for this type of problem is that it's the Engine Wiring Harness, Coil Packs, or MAF.

Since it appears to be the most common issue, I started with the Engine Wiring Harness. But, after checking the exposed sections of my harness it appears to be in pretty good shape (unlike the rotting/cracking pictures in other posts). I bought the car from a MB dealer in '98 with 30k miles on it, so the dealer may have already replaced the faulty harness.

Second, I replaced the spark plugs and cleaned the coils and MAF. Although this gave the car more pep, it doesn't appear to have cured the problem. Plus, I don't think it's a shorted coil pack since the car has a pretty smooth idle generally (other than problem #1).

I haven't been able to run a OBDII diagnostic test yet (not that those codes ever do me much good), but the only visually obvious engine issue is a leaky head gasket (leaking in the very front of the engine). Is it possible that the oil from the leaky head gasket is interfering with an electrical sensor (injectors or air)? Before changing the spark plugs I cleaned and degreased the engine so its pretty clean now but still has the same issues.

Please help. I'm fairly new to the DIY game, but can't fathom taking it to the dealer where they'll charge me more than the car is worth.

Thanks!!

Replace your OVP relay.

i have the same problem
 

Forgive my ignorance but what is the OVP relay?

Just type in OVP in the search box or Over Voltage Protection Relay.

You'll get more info to read than your brain can process. :)

Update: Following some advice, I changed the fuel pump relay ($25 @ ***************). This appears to have solved my initial two problems mentioned above (i.e. revs the RPM's while at a complete stop; or cuts out during acceleration or at speed), but now the car is suffering from two new issues:

1) Immediately after starting car RPM's fluctuate up and down (is "hunting" the correct term?). No roughness to it, just constant fluctuation between 500 and 1,500 RPM. Upon shifting out of "Park" this goes away, but returns upon next ignition start.
2) Upon heavy acceleration (usually from a complete stop) the engine will hesitate (maybe rumble a little) then kick in. No hesitation at normal throttle while moving.

I researched these issues and thought it may be the Overload Protection Relay so I replaced it ($58 @ ********az), which doesn't appear to have helped. I finally pulled the codes which revealed P0301 (misfire cyl. 1) and P0101 (MAF discrepancy). I'm hesitant to include the codes on this posting because I don't know how old they may be and I'd prefer advice based primarily off of the symptoms rather than codes (FYI... per previous post I did clean the MAF, but only want to replace as a last resort $$$).

Thanks again for your help! All of your advice is very much appreciated and I feel that I've already learned a ton from y'all about DYI car repair. Please let me know if you have any ideas on the new issues.

Thanks,
Sideshow76

Change the plug connectors under the coils..........
and make sure you don't have Plats

Remedy: After changing the fuel pump relay, overload protection relay, and fuel filter, to no avail, I finally got a new MAF. Replacing my MAF fixed the "hunting" idle and delayed acceleration issues. Work Time: 5 minutes; Cost: $184.37... Yippee!!

Special Thanks to all who contributed to help me diagnose the problem!

95 C-280 runs rough
 

I have a 95 C-280 with 170k and the same problems as described on your 96---idle "hunting" and cutting out and misfiring during acceleration. I have had the engine wiring harness, EGR valve, plugs (not platinum) and ignition wires replaced. Still suffering with the same symptoms. Most recently a tech found and repaired 2 vacuum leaks...did not solve problem. I had the MAF replaced but when the techs found it did not cure the problem they removed the new MAF and re-installed the old one at my request. We have spent a bunch of $$ trying to fix this and am running out of patience (and money). Any other suggestions?

p.s. there was evidence of mice chewing wires and vacuum hoses. The tech said to put whole cloves under the hood, in the trunk and under floor mats. He says the smell of the cloves irritates the rodents and will repel them.

Maf
 

Where did you obtain your MAF?

Cheapest I could find is at www.*************** for $185.

If your idle is "rough" (i.e. heavy vibration/shaking) rather than just "hunting" (i.e. bouncing RPM levels), then your problem may be an ignition coil rather than an MAF. They can cause similar symptoms (stuttering idle and delayed throttle response), but the ignition coil failure symptoms are much more pronounced and will cause a rough idle and possibly stalling.

You probably need a new MAF anyways, but if that doesn't fix the problem then check the ignition coil packs, which are attached to the top of 3 of the spark plugs (6 cyl). The ignition coils are very easily switched out (15 minute job) and cost about $65/each. While you're changing your coils you may also want to swap in a new set of spark plug wires ($60) and possibly spark plugs if they're old ($1-$3/each). My theory is that its best to swap out everything while you're in there to minimize the work later.

Hope this helps.

C-280 runs rough
 

We have replaced the plugs and wires, but not the coils or the connectors that go from the coil to the plug below it.

I will probably change those first since I have taken the engine cover off and am comfortable with working in this area.


2 different techs had switched the MAF but this did not solve the problem so the old one was re-installed.

By the way, should the MAF have 2 quick release clamps on it or one? Mine has one clamp on the top and none on the bottom.

Mine has two quick release clips, one on top and one on bottom of the side of the MAF connecting to the air intake filter box. The other side of the MAF is connected with a large worm-gear clamp.

C-280 coninued
 

I am missing a clamp

Could be a problem, as any unmetered air will result in wrong A/F mixture.The one that usually allows air is the one right at the throttle body end of the cross-over air pipe.

It is hard to get to , so guys forget about it...a real long screwdriver works well from the front...I check that one first as it is alway getting taken on/off [ like for plug changes and stuff]..so it is an automatic check.

C-280
 

I'll check that, too. Thanks


meanwhile I thinmk I will replace the 3 spark plug connectors that go to the coils. These have not been replaced ( they have M/B logos on them), even though I had the wires and plugs changed. If one of these connectors was faulty would it cause misifiring and skipping?

Coil to plug connectorsa are the FIRST misfire suspect on 104 HFM/SFI engines...by far...

C-280
 

I noticed that clamp- it's in a tough spot to get at.


Do you know of any good way to test spark plug to coil connectors and also the coils themselves ( i.e. volt/ohmeter, etc.)?

I can't keep buying parts and trying them out.. Thanks

The proper diagnosis is done with a secondary waveform from a Scope ..
But, most DIY do not have that equipment.
So, we tell them to change the coil to plug connectors under each coil as they are notorious for misfire and should be done as general maint.
Most Techs just change them when they do plugs b/c of their known misfire cuases.
Also, these systems don't like Plats at all, so consider the correct plugs.
If your plug connectors are old, I would just do them..at $4.00+ for gas,
you certainly need a well running engine..............

C-280
 

Thanks.

I just took the car out to runb a couple of local errands- maybe drove it for 10 miles or so. Guess what? No misfiring at all ! I swear these cars are possessed, or at least intermittently occupied by gremlins who delight in messing with us......

The problem is intermittant b/c of the type connection to the plugs from the connectors. Those 3 do not Snap onto the plug like the open ones do..they
are a compression spring and it is the coils placement that holds them down.
If you take one out, the thing to look for is the connection inside the connector that goes on top of the plug..if you see these are grayish colored , they have been arching and it is time to replace them..they take a beating b/c of this poor design in the connection and they are trapped in engine heat b/c of the coil on top , where the others are open to some breathing and heat dissipation..which is why they do not have the fail rate as the coil ones ..so , that's about it...a maint. item, just like the plugs.
One wants to remember that a coil fires TWO plugs on this type Waste Spark DIS system, so if the coil connector fails, the next plug is in series with that one so the misfire is amplified...along with the fact that the ECU is programmed to cut fuel to the injectors everytime it sees a misfire..so, no gas..compounding the skip....
See why we change them????
I would also check and see if you have the old part# OVP...that is ECU feed and a common intermittant problem..if it is the old #, chage it regardless or you will just get stuck when you don't want to be.

Yeah, with a SCOPE.
We are simply telling you the most possible suspects, according to experience and your complaint.
If you want a definitive diagnosis, buy a DSO Scope and it will tell you exactly what the ECU is seeing.

But you are a DIYer, so DIY info is :

Misfire on your car is commonly 3 plug connectors , OVP, wire harness , or incorrect plugs.
The connectors and OVP are not big $$$ and both are maint items anyway, so you are not throwing parts at it................ I always start with looking at the plug connectors and checking the OVP part #.

C-280
 

That would be the Over Voltage Protection relay, correct? I read about that in an earlier post....

this confirms my theory that once you open a can of worms, you need a much bigger can to put them all back in



thanks again

Yeah..
Do a Search on "OVP" and another on "Plug Connectors" and you will have enough info to fill a NY City phone book.
Mainly b/c, as I told you..they are Infamous for misfire failures..

..and your OVP had so much trouble that they Modified it and went with a different manufacturer to remedy the ongoing problem....so, why don't you just look and see if you have the old part# on your OVP..it is that simple.
..or, go and have a Dealer Scope it out for you. That will prob cost about 5 times what the connectors will ......

C-280
 

Where is the OVP physically located and what does it look like?


you should charge people (like me) for picking your brain.....

No , No charge...Free advice..so re-read it.
I just told you to use the Search Function for "OVP" .
And you come back with "Where is the OVP? "
You didn't read a word I said...
Do you want me to type all the OVP info that is already right at your keyboard ???

ALL the OVP related info in the WORLD is in the Archieves ...how else can I get this message to you ???

You want the part #'s... they are right there on your keyboard.......
Do you see the 'SEARCH" function on the top of the page??
Go here:

http://www.peachparts.com/shopforum/site-feedback/183547-how-do-i-search-information.html


http://catalog.peachparts.com/RenderScriptTemplate.epc?_cmd=epccat_VehicleAAA&cookieID=2EI1B4MYE2FF0U74DI&yearid=1996%40%401996&ma keid=MB%40%40MB%40%40X&modelid=C%2D280%2D001%40%40C+280+Sedan&catid=P%40%40Body+Electrical&mode=PA&s ubcatid=P2056@@Overload+Relay&source=www.peachparts.com&clientid=catalog.mercedesshop

I'm Done.